The paper that caused a bit of debate as to whether tides affect deposition in the Carboniferous Pennine Basin. Prior to this there was some evidence, but it was refuted by the main players. The tidal deposits themselves occur in discrete zones - within the TST of wide valley fills, and in mouthbar systems deposited during stillstand/ early TST.

1. Journal of the Geological Society, London, Vol. 159, 2002, pp. 379–391. Printed in Great Britain.
Identifying cryptic tidal influences within deltaic successions: an example from the
Marsdenian (Namurian) interval of the Pennine Basin, UK
1 1 1 2 3
M . J. B R E T T L E , D. M C I L ROY , T. E L L I OT T , S . J. DAV I E S & C . N. WAT E R S
1
Department of Earth Sciences, University of Liverpool, Brownlow Street, Liverpool L69 3GP, UK
(e-mail: m.j.brettle@liv.ac.uk)
2
Department of Geology, Bennett Building, University of Leicester, University Road, Leicester LE1 7RH, UK
3
British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK
Abstract: Research literature abounds on the depositional processes and products associated with macro-tidal
regimes, whereas there is little available literature on sediments deposited in micro-tidal regimes. This paper
presents new field-based sedimentological interpretations of the Marsdenian (Namurian, Carboniferous)
interval of the Pennine Basin, a basin-fill that is classically regarded as the archetypal fluvial-dominated delta
system. This paper reinterprets discrete lithostratigraphic units, and suggests they were deposited under the
influence of weak tidal currents. We highlight three lithofacies that contain tidally influenced deposits within
the Marsdenian interval of the Pennine Basin; a cross-bedded sandstone with mud drapes and reactivation
surfaces, a heterolithic ripple-laminated sandstone with muddy drapes and silty mudstone interlaminations,
and a rhythmic–parallel-bedded sandstone with mudstone–siltstone interlaminations. Evidence for cryptic
tidal signatures in tractionally transported and reworked sediments is qualitative, and largely dependent on the
sedimentologist’s view of what constitutes a diagnostic number of tidal indicators (i.e. mud-drape couplets,
reactivation surfaces). In areas away from either tractional deposition or reworking, sediments deposited from
suspension are more likely to preserve indicators of tidal processes. This paper focuses on a lithofacies
interpreted as a tidally influenced sand-rich delta-front mouthbar deposited from a buoyant effluent plume.
Time-series analysis of laminae thickness variations in this facies implies that these variations are rhythmic.
We review how the interaction of tidal currents and buoyant plume processes modifies depositional products.
This model implies that the rhythmic variation observed in the Marsdenian interval is attributed to the
modulation of plume deposition by tidal currents with a semi-diurnal and diurnal tidal periodicity.
Keywords: Marsdenian, Pennine Basin, deltaic sedimentation, tidal currents.
The characteristics of ancient macro-tidal successions have been stratigraphy, and are generally thought to represent the only
well documented in the sedimentological literature (Ginsburg intervals of marine influence during deposition of the otherwise
1975; Visser 1980; Allen 1981; Siegenthaler 1982; Demowbray fluvially dominated Namurian deltaic systems (Holdsworth &
& Visser 1984; Kvale et al. 1989; Williams 1989; Allen 1991; Collinson 1988). This paper, however, describes tidally influenced
Nio & Yang 1991; Read 1992; Martino & Sanderson 1993; facies that occur within sandstone delta cycles (Fig. 2), suggest-
Miller & Eriksson 1997; Adkins & Eriksson 1998; Greb & ing that the basin remained linked to oceanic waters for a greater
Archer 1998; Fenies et al. 1999), whereas investigations of period than that suggested solely by marine bands. Evidence for a
micro-tidal environments are mainly restricted to present-day tidal influence has been suggested in the Westphalian (Broadhurst
examples (e.g. Pejrup 1986, 1988; Allen 1991; Hughes et al. et al. 1980; Broadhurst 1988) and Namurian (Aitkenhead & Riley
1998; Makaske & Augustinus 1998; Fenies et al. 1999; 1996; Archer & Kvale 1997) intervals. In this paper we present
Johannesson et al. 2000; Hossain et al. 2001). The identification facies, time-series and stratigraphic data suggesting that tidal
of tidal signatures, either macro- or micro-tidal, in shallow-water currents influenced deposition during the Marsdenian interval,
marine systems is significant, as they constrain sedimentary and present models explaining the processes that may be
successions within a palaeogeographical and environmental zone. responsible for deposition within such micro-tidal regimes.
This is especially true when sequence stratigraphic concepts are The application of sequence stratigraphy in studying deltaic
applied, where there is a potential for the identification of incised systems, namely, the identification of sand-rich incised valleys
valley fills that often contain tidally influenced facies. and correlative interfluve areas, is well documented in the Upper
The delta systems of the Marsdenian interval form part of the Carboniferous units of northern England (Maynard 1992; Church
clastic infill of the northern Pennine Basin (Fig. 1), in which 1994; Church & Gawthorpe 1994; Hampson et al. 1996, 1997;
sedimentary provenance is inferred to have been dominantly from Wignall & Maynard 1996). In addition to the identification of
the north or NE (Drewery et al. 1987). The isolation of the tidal deposits, this paper places tidal deposits within a sequence
Pennine Basin from oceanic water masses is suggested to have stratigraphic context. We compare Marsdenian tidal deposits with
resulted in the absence of tidal currents from the Namurian existing tidally influenced valley-fill models (Allen 1991;
interval of northern England (Collinson 1988). The inference that Dalrymple et al. 1992; Allen & Posamentier 1993; Zaitlin et al.
tidal currents were not important has led to current interpretations 1994) and discuss the wider implications for the analysis of
of Namurian deltas being based on facies models generated from deltaic successions influenced by micro-tidal regimes.
river-dominated deltas. Regionally correlatable ammonoid- The data presented in this paper come from 42 borehole
bearing marine bands account for a thickness of ,5% of the records (mainly written descriptions dated between 1900 and the
379

2. 380 M . J. B R E T T L E E T A L .
extension during the northward-directed Rheno-Hercynian sub-
duction (Gawthorpe 1987; Leeder & McMahon 1988). Extension
produced a series of structurally high ‘blocks’ and basinal
depocentres (Lee 1988). These were part-filled by turbidite-
fronted deltaic systems during early Namurian to Kinderscoutian
time, with sediment supplied from the decaying Caledonian–
Appalachian Mountains (Collinson et al. 1977). The Marsdenian
interval marks the onset of a period of predominantly shallow-
water, mouthbar deposition. After Marsdenian time the younger
Yeadonian and Westphalian intervals record eventual infill of the
Pennine Basin and the development of coal-forming delta-top
swamp conditions (Guion & Fielding 1988; Guion et al. 1995;
Waters et al. 1996). Two mouthbar-dominated cyclothems are the
focus of this paper: the lithostratigraphic units that we will show
to be equivalent to the Readycon Dean Flags and Midgley–
Helmshore Grit (Brettle 2001). Both cyclothems possess region-
ally extensive regressive basal surfaces, with overlying tidally
influenced fluvial deposits and tidally influenced mouthbar
facies.
Tidally influenced deposits within the Marsdenian
interval
Previous research suggests that fluvial processes dominated
deposition in the late Namurian Pennine Basin, and that links
with open oceans were tenuous except at marine band intervals
(Collinson 1988). This paper describes three lithofacies that
suggest tidal processes operated in addition to fluvial processes
during the Marsdenian interval: (1) a cross-bedded sandstone
with mud drapes and reactivation surfaces; (2) a heterolithic
ripple-laminated sandstone with muddy drapes and silty mud-
stone interlaminations; (3) a rhythmic–parallel-bedded sandstone
with mudstone–siltstone interlaminations.
Lithofacies 1: cross-bedded sandstone with mud drapes
and reactivation surfaces
This lithofacies comprises coarse- to fine-grained sandstone with
disseminated granules and pebbles, and thin muddy drapes. This
lithofacies is similar to cross-bedded sandstone lithofacies within
which it is often interbedded, but is distinguished by the presence
of mud drapes on toeset and foreset surfaces, and a greater
abundance of reactivation surfaces within bed-sets (Fig. 4a). The
drapes comprise micaceous–muddy laminae that often, but not
always, occur in pairs, up to 5 mm apart. When traced, mud
drapes in some cross-bed sets occur in bundles that are
rhythmically spaced (Fig. 4b).
Fig. 1. Map illustrating the northern Pennine Basin, Marsdenian
exposure and the localities named in the text. Stratigraphic position of Interpretation: tidally influenced cross-bedded sandstone
the Marsdenian interval within the Carboniferous period with marine
band nomenclature is taken from Riley et al. (1993). Cross-bedded sandstone is ubiquitous within the Namurian
interval of the Pennine Basin, and is often very micaceous. This
facies distinguishes itself by the presence of paired muddy
present), five public-access wireline well data records (from drapes, bundles of mud drapes, and reactivation surfaces suggest-
petroleum exploration wells, dated from 1950 to the 1980s) and ing modulation of flow regime; potentially by either tidal
from more than 90 field localities (Fig. 1), from which logged processes (Nio & Yang 1991) or rapid changes in river dis-
sections, scaled field-sketches and facies analysis were con- charge.
structed (Fig. 3). Either allocyclic variations in fluvial discharge or the mouth-
ward progradation of the fluvial system may explain the inter-
bedded relationship of this facies with the cross-bedded
Pennine Basin geometry and stratigraphy
sandstone. If tidal processes were responsible for the formation
The geometry of the Pennine Basin during the Marsdenian of muddy drapes and reactivation surfaces, then the inertia
interval was inherited from Dinantian rifting, formed by back-arc associated with the basinward flow of a body of fluvial water

3. M A R S D E N I A N C RY P T I C T I DA L S I G NAT U R E S 381
Fig. 2. Schematic cross-section through
study area with current lithostratigraphic
units, facies associations and stratigraphic
position of Figs 4, 5, 7, 8, 9 and 10.
could have suppressed any tidal signature and allowed erosion of deposited dominantly directly from suspension, but was subject
sedimentary evidence for tidally influenced deposits. to frequent low-velocity currents and reworking. The variable
proportions of fine sandstone to siltstone may be dependent on
the proximity of the point of deposition to the locus of sediment
Lithofacies 2: heterolithic ripple-laminated sandstone
transport or local fluctuations in flow velocity. This facies
with muddy drapes and silty mudstone
represents deposition in a shallow-water mouthbar front, where
interlaminations
the substrate is affected by wave or current reworking in the
Within parts of the Helmshore Grit, lithofacies comprising thin shallow water depths. Current-ripple laminations with bimodal
parallel-laminated micaceous siltstone to fine-grained sandstone flow indicators represent periods of flow reversal during deposi-
interlaminated with grey to black micaceous silty mudstone are tion. Subtle laterally discontinuous reactivation surfaces are
common. These often overlie distal bayhead delta mouthbar subparallel to bedding, and are commonly truncated and over-
facies, and commonly have a sharp erosive base. Sedimentary lain by ripple structures. Bayhead mouthbars form thin and
structures are delicate, and comprise interlaminated fine-grained laterally extensive sheets in shallow water, where sediment entry
sandstone with a muddy siltstone matrix. Asymmetric starved points (either mouthbar feeder channels or crevasse splays) are
ripple cross-laminations with common flow reversals and sym- often close together (Van Heerden & Roberts 1988). The
metrical wave-ripples characterize these siltstones, whereas re- interaction of sediment input from several close entry points
activation surfaces are common in the sand-rich portions (Fig. 5). may provide conditions where flow reversals are generated.
Proportions of sandstone to siltstone can vary, and mica is Alternatively, flow reversals may have been caused by ebb and
abundant in both sandstone- and siltstone-rich components of flood tidal influences affecting the mouthbar front during
this lithofacies. The ichnofauna includes Planolites isp., Curvo- deposition. The ichnofauna suggests a brackish water column
lithus isp., Rosselia isp. and rare Chondrites isp. Similar (Eager et al. 1985), corroborating the interpretation of a tidal–
ichnofaunal assemblages have been described throughout the marine influenced depositional environment. The input of fluvial
Silesian deposits of the Pennine Basin (Eager et al. 1985), and waters into either brackish or marine waters suggests that
have been attributed to brackish environments. Fragments of flocculation may have been a significant mechanism responsible
carbonaceous debris are locally common. for the deposition of the clay-sized suspended fraction in such
environments.
Interpretation: tidally reworked bayhead mouthbar
deposits Tidal winnowing of mouthbar sediment
The layer-parallel, interlaminated fabric, high mica content and Whereas sediments deposited by plumes have a high preservation
small size of the cross-laminations imply that this facies was potential, those in the submerged mouthbar prodelta are con-

4. 382
M . J. B R E T T L E E T A L .
Fig. 3. A dip section through the R2a1–R2b3 succession (including the equivalent to the Alum Crag Grit, Readycon Dean Flags, East Carlton Grit, Woodhouse Flags and Scotland Flags) in the lower panel.
Marine bands R2b1, R2b2 and R2b3 form the datum levels for each correlated delta-lobe. The logged sections are: 1, Cowloughton Clough, Cowling (SD965420); 2, Clough Beck, Keighley (SE063433); 3,
Branshaw Quarry, Oakworth (SE032401); 4, Parkwood Quarries and Parkwood Brickpit, Keighley (SE065407); 5, Woodhouse Quarry, Haworth (SE062396); 6, Ponden Clough, Stanbury (SD981364); 7,
Wickering Crag, Haworth (SE048372); 8, Nan Scar Clough, Oxenhope (SE039336); 9, Rag Clough, Oxenhope (SE015336); 10, Middle Moor Clough, Crimsworth Dean (SE993336); 11, Nook Quarry,
Hebden Bridge (SE010275); 12, Fosters Delph Quarry, Mytholmroyd (SE022273); 13, Bare Clough, Luddenden Dean (SE018308); 14, Fulshaw Clough, Luddenden Dean (SE028301); 15, Cat-i-th well
Clough, Luddenden Dean (SE042282); 16, Triangle Rail Section, Ripponden (SE045212); 17, Noah Dale Core, Rishworth (SE019218; BGS borehole SE02SW23 with gamma-ray tool data); 18, Great
Clough, Scammonden (SE031147); 19, Pule Hill Section, Marsden (SE032100); 20, Leyzing Clough, Wessenden Head (SE 054064; National Geoscience Index Borehole reference number SE00NE7/BJ);
21, Wessenden Head Bore (SE062087); 22, Crowden Great Brook, Black Hill (SE083032); 23, Rake Dike, Holme Moss (SE101053); 24, Loftshaw Clough, Langsett Moor (SK170994); 25, Mouselow
Quarry, Glossop (SK024952).

5. M A R S D E N I A N C RY P T I C T I DA L S I G NAT U R E S 383
Fig. 4. Lithofacies 1: cross-bedded sandstone with mud
drapes and reactivation surfaces. (a) Trough cross-bedding
with bed set comprising double micaceous mudstone
drapes and reactivation surface (section oblique to foreset
dip). Similar lithologies occur in isolated examples
throughout the lower Marsdenian interval, suggesting a
cryptic tidal (ebb-dominated) influence. Slab from
Midgley Grit, Moselden Heights Quarry (SE044163). (b)
The planar cross-bedded set in the lower half of the image
has three zones with a number of muddy laminae. These
could be mud drapes deposited from suspension during
tidal slack water. ‘Mud-couplets’ as described by Visser
(1980) are not observed, probably because the ebb regime
dominates in such fluvial systems. The ebb cycle has a
high potential to erode mud drapes formed during slack
water and sandstones formed during subordinate current
stages (i.e. the weak asymmetrical tide of Nio & Yang
(1991)). Taken from Fosters Delph Quarry (SE022273)
(locality 29, Fig. 3).
Lithofacies 3: rhythmic–parallel-bedded sandstone
stantly reworked. This implies that although flow reversals are
with mudstone–siltstone interlaminations
common, cyclic laminated successions are rarely preserved. Tidal
processes constantly winnow the substrate surface in the sub- This lithofacies comprises fine- to medium-grained sandstone
merged mouthbar front, and resuspend mud and silt into the with a mudstone matrix, and interlaminations of mudstone and
water. Once suspended, landward movement of the water into siltstone. Lamination and bedding surfaces are subparallel,
shallower areas during the flood cycle forces the flow to whereas beds are massive, laterally persistent across exposures
accelerate the water column (Fig. 6) (Wiseman et al. 1986). The and range between 0.05 and 0.1 m in thickness (Figs. 7 and 8).
subsequent ebb cycle allows suspended sediment in the shallower Rare flute and tool marks are seen on bedding planes. Trace
water to return to deeper parts of the system, where it begins to fossils present in this lithofacies include Olivellites isp. and
settle through the water column. The reworking of the sand Pelecypodichnus isp.
bedload, in association with the settling of mud from suspension A good example of this lithofacies is seen at Kebroyd Bridge
during tidal slacks, deposits an interlaminated sand–mud lithol- (SE04452120), where an exposure with subhorizontal bedding
ogy. reveals cyclical variation in bed thickness on a centimetre and

6. 384 M . J. B R E T T L E E T A L .
Fig. 5. Lithofacies 2: (a) heterolithic
ripple-laminated sandstone with muddy
drapes and silty mudstone interlaminations.
(b) Slab of rock from Warland Wood
Quarry (SD947202; locality 6, Fig. 3)
revealing reverse ripple lamination, and a
back-flow ripple, that appears to have
grown up the lee slope of an older ripple.
This flow reversal, along with the
abundance of mud drapes, suggests a tidal
influence to this facies.
metre scale (Fig. 7). A repeated pairing, of 0.01 m scale, of have been interpreted as deposited by tidally influenced currents
thin–thick laminae is clear (Fig. 8), and can be seen on the (Broadhurst 1988; Read 1992; Aitkenhead & Riley 1996).
laminae thickness bar charts (Figs. 9, and 10b and c). On this To determine whether the laminae are truly cyclical, Fourier
scale, bed thickness varies from 0.02 to 0.1 m on a c. 25–28 bed time-series analysis is used to ascertain whether the succession
cycle, and individual beds commonly possess a micaceous silty contains periodic components. Fourier time-series analysis was
lamination (1–5 mm thickness) on their upper surface. The base run on sections 1 and 3 by A. Archer, using the same Fourier
of this lithofacies commonly lies either with a sharp contact or analysis program as was used to analyse Kinderscoutian sections
erosively on the silty interdistributary bay or offshore facies. The (Fig. 10b, c and e) (Archer & Kvale 1997). The short length of
upper surface is either truncated by shoaling mouthbar–distribu- the input data string, along with the apparently ‘noisy’ nature of
tary channel facies, or overlain by a flooding surface and the data, implies that the output of the Fourier transform is not
offshore marine–interdistributary facies. as refined as that of the Kinderscoutian sections. This is because
periodicities greater than 10 laminae cannot be resolved in the
sections detailed here, owing to the short length of the dataset.
Interpretation: tidally influenced sand-rich mouthbar Both datasets have similar ranges of harmonic output when
The dominance of layer-parallel bedding suggests this facies was compared with the Fourier transform results from laminae in the
deposited from suspension. Variations in sediment grain size are Kinderscoutian deposits, and the results of the analysis from
evident from the rapid spatial and temporal variations in the sections 1 and 3 share broadly similar peaks and troughs (Fig.
proportion of mudstone to siltstone. This facies is typical of 10e). The harmonic wave output of sections 1 and 3 falls into
sediments deposited in a mouthbar environment, where suspen- two frequency groups, of 1.9 2.6 and 3.6 4.4, suggesting an
sion-deposited sands are interbedded with rare tractionally trans- output equating approximately to two and four laminae.
ported sand (compare flute and tool marks). The cyclical laminae Although periodicities greater than 10 laminae cannot be
thickness variation seen at Kebroyd Bridge (SE04452120) sug- resolved because of the short length of the dataset, periodicities
gests a rhythmic fluctuation in the rate of suspension deposition. between the thickest laminae in sections 1 and 3 (43 and 48
It seems likely that either increased fluvial discharge or the laminae, respectively) may be invoked (Fig. 10b and c).
progradation of a fluvial channel over its associated mouthbar is
responsible for the presence of the large-scale internal scour
Processes occurring during deposition from an effluent
surfaces, rather than the subtle cyclic or paired laminae. These
plume and the influence of tides on a plume
broad scour features are overlain by cross-laminated sandstone,
implying high-flow discharge and the input of bedload-trans- We need to consider the processes that operate within the
ported sand. Similar facies have been described in the Carboni- mouthbar if we are to understand how tidal currents may
ferous sequences of the Pennines and the Appalachian Basin, and influence deposition from an effluent plume. Tidally influenced

7. M A R S D E N I A N C RY P T I C T I DA L S I G NAT U R E S 385
plume processes are not as well documented as models of tidally wedge (Nemec 1995). During periods of low discharge the saline
influenced duneform deposition (e.g. Visser 1980; Allen 1981). wedge is a significant feature, propagating 15–20 km upstream
Variations in the amount of fluvial effluent entering the basin from the outlet source, and being displaced from the channel
modulate the amount of sediment transported into the mouthbar only during periods of very high discharge (Wright & Coleman
(Fig. 11a). In basins with marine waters a ‘saline wedge’ forms 1974). Within the distributary channel the relatively static nature
during periods of low effluent velocity, when density difference of the saline wedge inhibits seaward bedload transport, and the
between plume and basinal waters allows underflow of the saline mixing of fluvial and marine waters creates turbulence and forces
the bedload into suspension (Nemec 1995). On the interface
between fluvial and marine waters, waves of turbulence (internal
waves) form, and these propagate mouthward. The increased
turbulence entrains bedload within the water column and carries
it to the mouthbar, where it is deposited (Ewing 1950; Wright &
Coleman 1974). If the internal waves within the plume are stable
features, the passage of alternating bodies of turbulent and non-
turbulent water may also have the potential to deposit rhythmi-
cally laminated sediment. As the plume passes over the shoaling
mouthbar and the saline wedge, it is compressed, undergoes a
hydraulic jump and becomes non-turbulent. The resultant ‘buoy-
ant plume’ creates a strong density layering, which is elongated
by the outward-flowing effluent, and carries sand-sized clasts into
the distal mouthbar (Wright 1977).
Tidal-current modulation influences the position of the saline
wedge within the outlet channel and therefore inertial force of
the plume (Fig. 11b). Flood tides suppress outflow as fluvial
water is banked up within the channel. In the Mississippi, periods
of high tide are shown to correlate with increased episodes of
crevasse splaying in the upstream fluvial system. This suggests
that tidal fluctuations can hold up fluvial outflow and lead to
banking up of water within the channel (Andorfer 1973). De-
creasing fluvial outflow forces vertical mixing within the chan-
nel, and allows the saline wedge to migrate upstream (Fig. 11a;
low discharge). This increases outflow turbulence, depositing
sediment in proximal mouthbar, and creating a headward shift in
grain-size distribution. During the ebb tide (Fig. 11b; ebb tide),
Fig. 6. Processes responsible for the development of lithofacies 2. The
the inertia of the outflowing plume is enhanced, creating a
ebb (a, e) and flood (c) tidal currents entrain bedload, and resuspend
mouthward shift in grain-size distribution. At periods of slack
clay-grade material, whereas the shallowing bay area amplifies the
velocity during the flood tide, further entraining and resuspending
water, increased mixing of the saline wedge with fluvial waters
sediment from the bay floor. Deposition of clay-grade material occurs from the distributary channel decreases effluent outflow rates,
during both high (b) and low (d) slacks. This may result in a gross accelerating flocculation of clay particles and their deposition
decrease in clay-grade material in the distal area, if tidal range is from suspension. The hypothetical grain-size distribution of a
sufficiently high and slack water durations are short. Modified from tidally modulated low-discharge plume (Fig. 11b) has the
Wiseman et al. (1986) and Nemec (1995). potential to generate the repeated thin–thick sandstone couplets
Fig. 7. Lithofacies 3: rhythmic–parallel-
bedded sandstone with mudstone–siltstone
interlaminations. Photomosaic of Kebroyd
Bridge locality (SE045213; locality 33, Fig.
3), showing unconformable base of ‘sharp
based’ mouthbar. Broad internal erosive
scours should be noted within the tidally
influenced sand-rich mouthbar, suggesting
erosion by fluvial processes during high
distributary discharge (asterisks denote
position of measured sections 2 and 3; see
Figs. 9 and 10).

8. 386 M . J. B R E T T L E E T A L .
Fig. 8. Example of lithofacies 3 at Kebroyd Bridge (SE045212). (a) Tidally influenced sand-rich mouthbar facies showing fine-grained sandstone
interlaminated with micaceous laminae and silty mudstone. (Note thinning of sand-rich laminae upwards, towards the centre of picture, followed by
marked thickening in the upper and lower parts.) (b) Close-up of a succession with thicker sandstone laminae. Beds occur in repeated thick–thin pairs. In
some examples the thin lamina forms a thin veneer less than 1 mm thick, bounded by a thin micaceous lamina.
Base of distributary
Distributary channel
channel
sandstone
increase
intensity of
increase in degree of
bioturbation
Chondrites current ripple
intense
50
lamination
50
bioturbation
40
40
Marker
40
bed
30
30
Laminae number
30
20
20
20
* Fig. 9. Graphic plot of laminae thickness,
for three sections at Kebroyd Bridge (see
Fig. 7 for position of these sections).
10
10
10
Marker beds represent beds traced laterally
Marker along the exposure; these reveal a thinning
bed in the middle of section 2 by six sandstone
60
50
40
30
20
10
0
60
50
40
30
20
10
0
60
50
40
30
20
10
0
Lamina thickness (mm) Lamina thickness (mm) Lamina thickness (mm) ‘Sharp-based laminae. This may represent removal by
mouthbar erosion during periods of high discharge.
Kebroyd Bridge Kebroyd Bridge Kebroyd Bridge (see Figure 7) Asterisk denotes position of image in Fig.
section 1 section 2 section 3 8a.
with intercalated silty mudstone laminae seen in the Marsdenian extent the flood tide), with the sand-rich component being
field examples (Figs. 8–10). rapidly deposited during periods of waning flow. The mud and
The grain size of sediment in the fluvial channel also controls silt fractions are deposited during periods of either no or very
laminae thickness characteristics in the sediment. In the case of low flow regime (i.e. during tidal slack water).
the Marsdenian mouthbar facies, the sediment has a bimodal Within plume deposits, thick–thin pairs of sandstone laminae
grain size, comprising very fine- to medium-grained sandstone are formed by the ebb and flood cycles within a single semi-
and siltstone or silty mudstone, which is commonly rich in mica diurnal tidal cycle, with the thicker sandstone laminae interpreted
flakes. Whereas the muddier component of this sediment is to have been deposited during the ebb stage (Fig. 11b). During
carried in suspension, the coarser, sand-rich portion is carried by the ebb period, flow regime increases as fluvial inertia and
either tractional or mixed saltation–suspension processes. By outgoing tide both flow in a downstream direction. The resultant
inference, both mud and sand components are transported during higher flow regime increases the amount of entrained coarser
periods of higher flow regime (i.e. the ebb tide, and to a lesser clastic sediment (typically very fine- to medium-grained sand-

9. M A R S D E N I A N C RY P T I C T I DA L S I G NAT U R E S 387
20
(a) 0
10 20 30 40 50 60 70 80 90
lamina number
60
43 lamina
40
20
(b) 0
10 20 30 40 50
lamina number
40 48 lamina
20
(c)
0
10 20 30 40 50
lamina number
(d) 10 19.61
(Archer & Kvale, 1997)
power spectral
density
5 30.30 2.35-2.07
8.93
5.0-4.6 2.86-2.67
0
0 0.1 0.2 0.3 0.4 Fig. 10. Fourier analysis of lithofacies 3
frequency corresponding
laminae cyclicity. (a) Bar chart of thickness
range of sand-rich mouthbar facies laminae, from
(this study) (Archer & Aitkenhead & Riley (1996). Hag Farm
Kvale, 1997)
(e) 20 1.9- 2.6 2.07- 2.86
Borehole (Kinderscoutian), near Keighley,
3.6- 4.4 4.6- 5.0 Yorkshire, UK. (b, c) Bar charts showing
power spectral
10 thickness of mouthbar facies laminae from
density
1.3 (this study) sections 1 and 3 of the Kebroyd Bridge
2.6 both =1.9
0 section (Fig. 9). Drawn to the same scale as
3.6 2.4
4.4 1.2 the bar chart of Aitkenhead & Riley (1996).
-10 (d) Fourier analysis plot of data from (a) by
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Archer & Kvale (1997). (e) Fourier analysis
frequency plot of data from (b) and (c) by A. Archer
Key for v) (University of Kansas), and corresponding
Kebroyd Bridge Section 1 ranges between this dataset and that
Kebroyd Bridge Section 3 displayed in (d).
stone), and creates a seaward shift in the distribution of fine- to weaker, or subordinate tide, is formed by centripetal forces as the
medium-grained sandstone. When the tide is at its lowest slack Earth rotates and pushes the ocean surface away from the Earth.
water, the lack of flow allows deposition of mudstone, or more The dichotomy in tidal range during a 24 h period is known as
commonly in the Marsdenian deposits, a micaceous veneer when the diurnal inequality. When this is applied to the model of
viewed on laminae planes (Fig. 11b; low slack). The flood tide tidally influenced plume deposition, diurnal inequality should
reworks underlying deposits, which are deposited as the tidal generate a periodicity of four, as it occurs over two semi-diurnal
flow wanes, creating a thin muddy sandstone lamina that is periods. Diurnal inequality should produce a thin–thick cyclicity
almost always thinner than the sandstone lamina deposited by the in alternate semi-diurnal tidal units (Fig. 12a), as the dominant
ebb current. At high-tide slack water a second mudstone or a tide produces thicker sandstone laminae pairs and the subordi-
micaceous lamina is deposited, completing the thick–thin, or nate tide produces thinner sandstone laminae pairs.
semi-diurnal tidal cycle (Fig. 11b; high slack). Therefore, any set As the Moon rotates around the Earth, the Sun and the Moon
of mouthbar deposits influenced by tidal processes may possess fall into alignment (or syzygy) or lie perpendicular (or in
sandstone laminae producing repeated periodicities of two (Fig. quadrature), on a 14 day periodicity (Fig. 12b). When the Sun
11b; logs A and B). and Moon are in alignment, the tidal bulge is amplified by up to
On any point of the Earth’s surface, two gravitational maxima 30%, increasing tidal ranges and creating stronger (or spring)
pass in any 24 h period, creating two semi-diurnal tidal bulges of ebb and flood tides. When the Sun–Moon system is in quad-
different magnitudes that are generated independently of each rature relative to the Earth, the combined gravitational forces are
other. The stronger, or dominant, tide is created by the gravita- not as strong, and the resultant tidal bulge is smaller, creating
tional pull of the Moon on the ocean surface, whereas the weaker (or neap) tides. Therefore, when 28 or more semi-diurnal

10. 388 M . J. B R E T T L E E T A L .
Fig. 11. Processes responsible for the development of a cyclic tidal signature in heterolithic mouthbar facies (after Nemec 1995). Only during the lowest
river discharges, when the saline wedge propagates headward allowing the lofting of sediment, do tidal currents enhance or suppress river outflow to the
extent that it influences the rate of deposition and grain size deposited.
units appear in a stacked succession of tidally influenced plume thick–thin–thick cycles over 43 and 48 laminae for sections 1
deposits, and no hiatal or erosive surfaces are present, it may be and 3 is suggestive of a spring–neap–spring cyclicity. Assuming
possible to resolve a cyclical motif associated with lunar this represents a 14 day lunar cycle, the absence of a full set of
precession. When deposition is influenced by a spring–neap 56 laminae may be due to reworking and erosion by fluvial
cycle, periodicities of 56 laminae are expected (representing 28 processes, which can be demonstrated by the presence of scour
semi-diurnal cycles deposited over 14 days). Deviations from the features (Fig. 7). Conversely, the number of days in a lunar
expected cyclicity may occur in association with increased fluvial month was marginally greater in the past (c. 30.5 Æ 1.5 during
discharge. In these circumstances, erosion of the substrate leads Precambrian time compared with 28.5 at the present day
to stripping of laminae and the generation of discontinuities (Williams 1989), suggesting that more than 56 laminae would be
within the tidal mouthbar unit. Therefore, if a plume is tidally expected within the spring–neap–spring cycle. The critical
influenced, cyclicity in sandstone laminae should be observed on observation remains, however: that laminae systematically occur
a semi-diurnal (two), a diurnal (four) and half-lunar monthly (56) in repeating sets of two (indicating semi-diurnal tides) and four
periodicities. (indicating unequal semi-diurnal tides) with characteristic thick-
ness variations. The integration of Fourier time-series analysis
and the model for a tidally influenced mouthbar provides a useful
Discussion: the significance of identifying cryptic tidal tool for the identification of cryptic tidal signatures within plume
influences and its significance in the Carboniferous deposits. Such deposits have a higher preservation potential than
sequence of the UK sediments deposited within areas where higher flow regimes
The observation of systematic bed thickness variations has could either rework or erode part of the succession.
suggested a tidal influence during mouthbar deposition, without The effect of tidal processes in settings dominated by macro-
the necessity of identifying the presence of mudstone drapes. tidal ranges is well documented in modern deltas (Wright &
Comparing results of the Fourier transform and the model for Coleman 1973, 1974; Coleman & Wright 1975; Galloway 1975;
tidally influenced plume deposition suggests that laminae peri- Coleman 1981; Wiseman et al. 1986; Allen 1991), whereas the
odicities of two and four represent semi-diurnal tides and subtle influence of tidal processes on areas with lesser tidal
unequal semi-diurnal tides over a diurnal period. The presence of ranges is underrepresented in modern and ancient sedimentologi-

11. M A R S D E N I A N C RY P T I C T I DA L S I G NAT U R E S 389
Fig. 12. Model representing the
depositional patterns expected from the
tidally influenced plume during a diurnal
and lunar 14 day cycle. Approximately
every 24 h, any point on the Earth’s surface
is influenced by two tides (a): a dominant
tide created by the pull of the Moon, and a
subordinate tide produced by centripetal
forces that push the ocean surface away
from the land. The differing tidal strengths
are expressed by thinner (subordinate tide)
or thicker (dominant tide) semi-diurnal
units. The Moon revolves around the Earth
every 28 days. During this period it either
lies in alignment with the Sun (syzygy) or
perpendicular to it (quadrature) (b). During
alignment the combined gravitational pull
of the Sun and Moon increases tidal bulges,
generating a spring tide. When the Sun and
Moon are at quadrature, the combined
gravitational pull is less, and a weaker or
neap tide occurs. Tidal ranges are greater
during the spring tide, and tidally
influenced mouthbar laminae occur in thin–
thick packages every 56 tidal laminae (or
28 semi-diurnal laminae), equivalent to a
14 day period.
cal literature. The presence or absence of a tidal regime may
Conclusions
have significant connotations for interpretation of sedimentary
systems, regardless of the size of the tidal range. Tidal regimes The Namurian Pennine Basin has been interpreted by many
have a significant effect on the coastline geometry (Wright & workers as an example of the quintessential fluvial-dominated
Coleman 1973, 1974; Coleman & Wright 1975), grain-size delta. It has been suggested by most previous studies that the
distribution at river mouths, or the cleaning or winnowing of Pennine Basin was geographically restricted from oceanic waters
clay-grade particles from a succession (Orton & Reading 1993). and that tidal reworking had no effect on the deposition of
This may be particularly true with respect to the degree of clay Namurian deltas. This paper has identified a stratigraphic interval
redistribution that may occur in settings influenced by micro-tidal within the Namurian interval of the Pennine Basin that contains
regimes (i.e. Fig. 6). facies that are influenced by tidal processes. We have identified
Amplification of tidal range within an incised valley may facies within the Namurian interval that demonstrate tidal
explain how one might expect a tidal current to be amplified processes operated, and that the Pennine Basin must therefore
(Allen & Posamentier 1993); but it does not take into account have been connected to oceanic waters throughout deposition
the complexity of depositional processes that occur within the and not only during marine band deposition. This new interpreta-
valley; specifically, the influence of tidal processes on mouthbar tion requires that existing palaeogeographies are reassessed and
plume deposits, especially when involving the mixing of saline implies that alternative depositional models should be sought for
and non-saline waters in a fluvial regime that may be fluctuating the Namurian interval.
in discharge (Wright & Coleman 1974; Nemec 1995; Hughes et The identification of cryptic tidal facies similar to those
al. 1998a). The use of mud drapes and reactivation surfaces as described here in other basins may be useful in aiding the
evidence for tidal influences is well reported (Ginsburg 1975; identification of tidally influenced systems and ascertaining the
Visser 1980; Allen 1981; Siegenthaler 1982; Demowbray & true extent of palaeogeographical connectivity with oceanic
Visser 1984; Nio & Yang 1991), but such structures may be water masses.
absent in micro-tidal regimes or areas with low deposition rates.
Within mouthbar-dominated incised valley fills the examination These findings form part of the Ph.D. thesis of the principal author. Thanks
of successions deposited by plumes may reveal the presence of are due to J. Bagshaw for access to Fletcher Bank Quarry (Marshalls), A.
tidal currents. Archer (University of Kansas) for running Fourier analyses on the datasets
described in this paper, N. Riley and J. Macquaker for their critical
Tidal deposits have been recognized in Southern North Sea
reviews and A. Nuttall for assistance in the field.
facies (O’Mara et al. 1999), whereas they have not in onshore
outcrop (Collinson 1988). To ascertain that tidal currents influ-
enced the Namurian Pennine Basin is regionally significant, as it
confirms that selected onshore depositional systems form analo-
Appendix: localities with examples of lithofacies 1–3
gues for Carboniferous Southern North Sea reservoirs (Hampson Examples of lithofacies 1 are observed at in the Woodhouse
et al. 1997, 1999). Flags at Fosters Delph Quarry (SE022273; locality 12, Figs 3

12. 390 M . J. B R E T T L E E T A L .
and 4a), the Midgley Grit at Moselden Heights Quarry, Scam- Carboniferous) deltaic sediments of the Central Pennine Basin, England. In:
monden (SE043164; Fig. 4b) and the Midgley and Helmshore Curran, H.A. (ed.) Biogenic Structures, their Use in Interpreting Deposi-
tional Environments. Society for Economic Paleontologists and Mineralogists,
Grit at Fletcher Bank Quarries, Ramsbottom (SD805164). Special Publications, 35, 99–149.
Examples of lithofacies 2 are observed in the Helmshore Grit Ewing, G.C. 1950. Slicks, surface films and internal waves. Journal of Marine
at the upper part of Whittle-le-Woods Quarry (SD584217), Research, 9, 161–187.
Warland Wood Quarry (SD947202), Harper Clough Delph Fenies, H., De Resseguier, A. & Tastet, J.P. 1999. Intertidal clay-drape couplets
(Gironde estuary, France). Sedimentology, 46, 1–15.
(SD716317) and Fletcher Bank Quarries, Ramsbottom
Galloway, W.E. 1975. Process framework for describing the morphologic and
(SD805164). stratigraphic evolution of deltaic depositional systems. In: Broussard, M.L.
Examples of lithofacies 3 are observed in the equivalent of the (ed.) Deltas: Models for Exploration. Houston Geological Society, Houston,
Alum Crag Grit at Kebroyd Bridge (SE044212; locality 16, Fig. TX, 87–98.
3) and in the equivalent of the Alum Crag Grit and the Readycon Gawthorpe, R.L. 1987. Tectono-sedimentary evolution of the Bowland Basin,
northern England, during the Dinantian. Journal of the Geological Society,
Dean Flags of the Noah Dale Core, Rishworth (SE019217; London, 144, 59–71.
locality 17, Fig. 3). Ginsburg, R.N. 1975. Tidal Deposits: a Casebook of Recent Examples and Fossil
Counterparts. Springer, Berlin.
Greb, S.F. & Archer, A.W. 1998. Annual sedimentation cycles in rhythmites of
Carboniferous tidal channels. In: Alexander, C.R., Davies, R.A. & Henry,
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Received 30 May 2001; revised typescript accepted 14 February 2002.
Scientific editing by Joe Macquaker